class Solution {
         int dx[4]={1,-1,0,0};
     int dy[4]={0,0,1,-1};
     int m,n;
public:
    void solve(vector<vector<char>>& board) {
        m=board.size(),n=board[0].size();

        for(int j=0;j<n;j++)
        {
            if(board[0][j]=='O')dfs(board,0,j);
            if(board[m-1][j]=='O')dfs(board,m-1,j);
        }
        for(int i=0;i<m;i++)
        {
            if(board[i][0]=='O')dfs(board,i,0);
            if(board[i][n-1]=='O')dfs(board,i,n-1);
        }

        for(int i=0;i<m;i++)
            for(int j=0;j<n;j++)
            {
                if(board[i][j]=='.')board[i][j]='O';
                else if(board[i][j]=='O')board[i][j]='X';

            }
    }

    void dfs(vector<vector<char>>& board,int i,int j)
    {
        board[i][j]='.';
        for(int k=0;k<4;k++)
        {
            int x=i+dx[k],y=j+dy[k];
            if(x>=0 && x<m && y>=0 && y<n
            && board[x][y]=='O')
            {
                dfs(board,x,y);
            }
        }
    }
};
